This invention relates to a process for the manufacture of a high-chromium iron alloy which contains a total of not less than 90% by weight of chromium and iron, the Cr/Fe weight ratio being not less than 4.0, and not more than 10% by weight of carbon plus a trace of impurities. This iron alloy is useful as an additive for alloys having small iron content.
As the additive for this purpose, there has heretofore been used metallic chromium. Metallic chromium is chiefly produced by the so-called thermit process involving reduction of chromium oxide such as with aluminum or silicon or by the process involving electrolysis of an aqueous solution. Whichever process may be used, the production is so costly that uses found for the product have been rather limited.
Many of the chromium-containing alloys tolerate inclusion of small amounts of iron. Particularly in recent years, as the development of uses has gained in scope, the ability of chromium-based alloys containing small amounts of iron to resist heat and corrosion has come to attract attention. Consequently, the demand for such alloys is steadily on the increase.
A process whereby a mixture consisting of chromium and iron at a ratio of about 3 is obtained from a chromium ore having small chromium and iron contents and a small Cr/Fe ratio has been disclosed by U.S. Pat. No. 2,971,834. From a chromium ore which has a chromium content of 30% and an iron content of 19% and therfore has a Cr/Fe ratio of about 1.6, for example, this process produces a slag containing chromium and iron at a Cr/Fe ratio of about 3.1 and a metal alloy having an iron content of 83% and a chromium content of about 15% by reducing said chromium ore with a silicon reducing agent.
The present invention, in contrast, is characterized by the fact that it produces a high-chromium iron alloy having a total of not less than 90% of chromium and iron contents and therefore having a Cr/Fe weight ratio of not less than 4.0 and also by the fact that said iron alloy contains impurities such as P, Ni and Co in negligibly small amounts. Thus, the present invention constitutes a technique which has never existed in the prior art.
An object of the present invention is to provide a highly economical process for the manufacture of a high-chromium iron alloy which proves to be useful as an additive for alloys of small iron contents.